The present invention relates to a part holder particularly for workstations or machining centers with a revolving table.
It is known that the evolution of machine tools for the machining of metal and nonmetallic parts by chip-forming has led to the production of increasingly complicated and sophisticated workstations in which it is possible to subject the parts to various machining operations. More particularly, these workstations are usually provided with a holder that is substantially shaped like a parallelepiped with a square base, and the parts to be machined are rigidly coupled, by virtue of suitable locking devices, to the lateral faces of said holder, so that the tools of the workstation, which are appropriately moved along at least two mutually perpendicular axes, can reach the parts with high precision and machine them.
Some workstations include a table which generally revolves about a vertical axis and on which the holder is placed so that the tools can move towards the parts mounted on the holder not only by virtue of the movement of said tools but also by virtue of the rotation of the holder about said vertical axis.
Workstations obviously require considerable investments which can be amortized, and thus lead to an economically advantageous activity, only if machining downtimes, such as for example the time required to mount the parts on the holder or remove them from it, are minimized.
The current trend is to provide holders that can carry a large number of parts and to have at least two holders, also known as pallets, which are alternately placed on the revolving table of the workstation. In this manner, while the workstation is machining one batch of parts, it is possible to mount the next batch of parts on the other holder, which replaces the first one once its parts have been machined. In this way it is possible to minimize machining downtimes but there is the drawback of having to purchase two or more holders which are relatively expensive because they are very high precision products.
In some cases it is also necessary to manufacture a special holder for particular parts to be machined. In such cases, the holder, after a small number of runs, is generally stored until the next request for special parts. In this case, in addition to the high purchase cost of such holders, there is also the problem of additional costs, that is to say losses, linked to nonuse of the holder.
Another drawback that can be observed in the use of currently commercially available holders, in which the parts to be machined must be mounted on the lateral faces of said holder, is constituted by the fact that the operator encounters some difficulty in locking the parts as they tend to move, due to their weight, during this operation.